The present invention is directed toward the field of power management systems. In particular, a load management system is disclosed for use with remotely powered electronic or telecommunication devices. Remotely powered devices generally receive power from a power source located some distance away through high voltage powering wires. Power converters located within the remote device convert the high voltage received from the power source to lower voltage levels that are compatible with the electronics within the remote device. The load management system of the present invention manages the load on the power converters to insure their proper functioning.
Because of the resistance in the powering wires in a remotely powered system, the voltage that the power source is able to deliver (xe2x80x9cload voltagexe2x80x9d) to the power converters is limited by the current required by the power converters (xe2x80x9cload currentxe2x80x9d). That is, as the load current increases, the load voltage decreases. The power delivered to the power converters (xe2x80x9cload powerxe2x80x9d) will increase in response to increased load current demand until the load current reaches a threshold level. Once the load current reaches the threshold level, any further increases in the load current will actually result in a decrease of the deliverable load power due to power losses in the powering wires. If the load current increases further, a point may be reached in which the power required by the power converters exceeds the delivered load power. When this happens, the power converters will enter an unsustainable state and behave erratically. This can cause the remote device to behave erratically.
An exemplary remotely powered electronic device is an Optical Network Unit (xe2x80x9cONUxe2x80x9d). An ONU is a device that is used as an interface between fiber optic telecommunication lines and traditional wires used to provide telecommunication services such as cable television and telephonic services to homes or other buildings. The ONU has a power supply that typically includes: (i) input protection and filter circuitry; (ii) energy storage circuitry, (iii) input voltage monitors and threshold circuitry, (iv) D.C. to D.C. power converters; (v) ringing generators; and (vi) alarm and digital interface circuitry.
At an installed ONU, the load current demand varies depending on the customers"" telecommunication service usage. The powering system is engineered to provide adequate power to the ONU under expected peak load current demand conditions. But, there could be times when the power demand of the ONU could exceed the load power available to the ONU. If that occurs, power converters in the ONU may behave erratically.
To prevent the remote device from behaving erratically, many remote devices shut down when the power demands exceed the power available. In the case of an ONU, a complete shut down would result in a complete interruption of all telecommunication services and is a very drastic solution to the problem. It is, thus, desirable to provide a system for preventing erratic ONU behavior without completely shutting down all telecommunication services.
Therefore, there remains a need for a load management system that will protect against erratic behavior without shutting down all functions or services.
The present invention overcomes the problem noted above and satisfies the needs in this field for a load management system that protects against erratic power converter behavior. It is therefore an object of the load management system of the present invention to shed load, in a systematic manner, as the load demand approaches the maximum-available-power point so that erratic power behavior may be avoided. It is a further object to provide a power management system that shuts down preselected load elements when the delivered load voltage falls below certain threshold levels and turns on load elements that had been shut down when the delivered load voltage rises above other threshold levels.
The power management system of the present invention turns off preselected load elements in a sequenced manner to allow the delivered load voltage to recover from a low voltage level to a voltage level that will insure stable power converter operation without completely shutting down all of the power converters. The load management system provides control signals to turn off certain load elements when the delivered load voltage falls below certain threshold levels. The load management system, through the control signals, signals the load elements to resume operation after the delivered load voltage has risen above other threshold levels.
The load management system of the present invention includes sensing means for monitoring the delivered load voltage, means for causing specific load elements to shut off when the delivered load voltage drops below certain thresholds, and means for causing those load elements to reactivate when the delivered load voltage rises above other thresholds. In one embodiment the load management system includes a number of hysteresis circuits, each hysteresis circuit comprising a first state sensing circuit, a second state sensing circuit, and a state transition circuit. The state sensing circuits could comprise comparators and the state transition circuit could comprise digital logic and memory elements. The state sensing circuits sense when the output voltage reaches certain thresholds and communicates this to the state transition circuits which in turn cause specific load elements to turn on or off.
As will be appreciated, the invention is capable of other and different embodiments, and its several details are capable of modifications in various respect, all without departing from the spirit of the invention. Accordingly, the drawings and description of the preferred embodiment are to be regarded as illustrative in nature and not restrictive.